Effect of cold acclimation and rapid cold hardiness on cold tolerance and cryoprotectants of the greenbug Schizaphis graminum (Hemiptera: Aphididae)

Insects can increase their survival at subzero temperatures, prior to long or short term exposure, to non-lethal cold temperatures by cold acclimation (ACC) or rapid cold hardiness (RCH). In this research, the effect of rapid or gradual decrease in temperatureon cold tolerance of adults of the greenbug, Schizaphis graminum (Rondani) was investigated. LT50 (lower lethal temperature for 50% mortality) of aphids acclimated at 10 °C for one week showed no significant differences with control (aphids reared at 20 °C). In addition to the cold acclimation, adults of S. graminum showed RCH response too.When the rearing aphids at 20 °C were transferred directlyto a range of sub-zero temperatures for 2 h, LT80 (lower lethal temperature for 80% mortality) was -11.6 °C, but acclimation at 0 °C for 5 h before transfer to -11.6 °C, induced maximum RCH, led to increase of survival to 73%. RCH was induced by cooling of the insects at 0 °C for different rates.Maximum survival (66%) was achieved by cooling at 0.05 °C/min. Accumulationof sugars and polyols is one of the major mechanismsunderlying ACC and RCH. In this study, trehalose and glucose increased considerably through ACC and RCH treatments, suggesting the role of these compounds in increasing cold tolerance of S. graminum.